COOPERATIVE CYANIDE DISSOCIATION FROM FERROUS HEMOGLOBIN

Massimo Castagnola, M Brunori, G Antonini, A Bellelli

Risultato della ricerca: Contributo in rivistaArticolo in rivista

34 Citazioni (Scopus)

Abstract

Rapid reduction of cyano-met hemoglobin (Hb+CN-) leads to the formation of an intermediate species, the cyanide derivative of ferrous hemoglobin, which dissociates to unliganded hemoglobin because of the extremely low affinity of the ligand for the ferrous heme iron. The properties of the intermediate were studied by transient spectroscopy in human hemoglobin and its isolated alpha and beta-chains, in the presence and absence of CO. When mixing with dithionite, the time courses of reduction of the heme iron and dissociation of cyanide overlap considerably; addition to the reaction mixture of the redox indicator methyl viologen considerably increases the rate of reduction and allows unequivocal determination of the spectroscopic and kinetic properties of the intermediate. The results show that (i) the dissociation of cyanide from the isolated alpha and beta-chains (as well as the (alpha-CO)2(beta+CN-)2 hybrid) is a simple process; (ii) the two chains display similar rate parameters, but show spectroscopic inequivalence, both in the Soret and the visible regions; (iii) cooperative effects are shown to control the rate of dissociation of cyanide from hemoglobin, similarly to what happens for oxygen; and (iv) allosteric effectors (typically inositol hexaphosphate)increase the overall rate of dissociation by stabilization of the T state. We have, therefore, shown for the first time that the dissociation of cyanide from ferrous hemoglobin is controlled by the quaternary state, thereby adding one more ligand to the analysis of the structure-function relationships in hemoglobin.
Lingua originaleEnglish
pagine (da-a)2258-2263
Numero di pagine6
RivistaTHE JOURNAL OF BIOLOGICAL CHEMISTRY
Volume267
Stato di pubblicazionePubblicato - 1992

Keywords

  • HEMOGLOBIN

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